Arrangement for prevention of reverse current in battery chargers



ARRANGEMENT FOR PREVENTION OF REVERSE CURRENT IN BATTERY CHARGERS Filed Jan, 9, 1928 Discharge Charge Curre n t 5 ggljichmidt y fifth/Z9 Patented June 11, 1929.

umrrn FSTLATIES' PATENT OFFICE.

KARL SCHMIDT, OF BERLIN-EIGHTENRADE, GERMANY.

Application filed January s, 1928, Serial No.

My invention relates to an arrangement for prevention of reverse current in battery chargers.

It is well known that there ar'e'difliculties with all arrangements for converting alternating current into direct current when usedfor chargingbatteries. \Vhen alternating current is rectified into direct current the voltage is pulsating. If a gas rectifier is lo'used, then this pulsating voltage may be used directly for charging batteries, because due to the valve action of the gas rectifier a reverse current is impossible.

It is different, however, with a mechanical rectifier, e. g., of the well-known pendulum type. Here a reversal of battery current may take place through the rectifier wherever the instantaneous value of the pulsating pressure is below the battery pressure. The

result of this is an aggravated spark at the contact points and the difiiculty, or even impossibility, s of charging all batteries.

This can be overcome in a way by adjusting.

the arrangement so that the circuit is opened at the instant when the pulsating pressure is equal to the battery pressure. All of 1 these arrangements depend however on a definite pressure, and must therefore be changed, depending on the strength of current. i

The invention is further illustrated in the accompanying drawings in which Figure 1 is adiagram illustrating the relation of the pulsating voltage and the battery voltage.

Figure 2 is an illustration of the manner in which this invention overcomes the ditficulties of the reverse current, and

Figure 3 is a diagrammatic representation of the saturating characteristics of the 40 choke coil employed in this invention.

In Fig. 1 the curve 0 a e b d represents a rectified/alternating current wave corresponding to one-half period of the rectification by meansof a mechanical rectifier as,

for instance, the one illustrated in Fig. 2. Furthermore, E?) is the battery pressure. It will be seen that at a point 0 the pulsating pressure is zero, while the battery pressure is its -full value. The result is that at point c a maximum current from flow in the reverse direction through the rectifying apparatus and this will gradually decrease until point a is reached. At point a the battery pressure is equal to the pulsating pressure; the discharge or charge current is also Zero. From pointc on the charging presis reached.

brought to the 245,612, and inGermany January 27, 1927.

sure is larger than the battery pressure and consequently an increasing charge will occur until point e, which will fall off to zero at point I). At this point a discharge of the battery will again take place until point d Thus, in order to charge a battery the charging device must be so arranged that the-charging connection is made at point a and broken at point I).

Employing my invention, it will not be necessary to take account of the above procedure. The charging arrangement may be used with any pressure or current. The 7 principle of the invention consists substantially in the fact that a choke is connected in the charging circuit which reduces as far as possible any variations in the pulsating current, and which reduces the reverse current from the battery through the rectifier to the lowest possible value. According to the invention, an-iron core coil may be used saturated by means of direct current in such a way that the current flowing into the battery will meet with little impedance on account/s0 4 of the saturation, while the reverse current on account of demagnetization of the iron core will meet with high inductive impedance. I

In Fig. 2 a suitable scheme of connection is illustrated, according to the invention. A and B are the supply terminals to which rectifying apparatus. with contacts K and K are connected. The contacts workin such a way that orilyone half wave is al- 9 lowed to go through, while at the other half wave the contacts are opened. This is done by means of a small cam driven synchronously with the alternating current to be. rectified, by means of a small synchronous 5 motor. This cam controls contact springs F} and F In the charging circuit itself there is a choke coil D with saturated iron core, a primary winding P, and a battery Q to be charged. Parallel with the battery there may be supplied a direct current saturating winding S on the coil in connection with a choke coil V and a regulating resistance R. R serves to secure the proper saturation and V to prevent the passage of alternating current generated in the main choke coil into the battery.

Fig. 3 illustrates the well-known saturation curve of a choke coil according to the invention. This may be, for instance,

point P by a constant magnetizlng current 13,. At thispoint saturation beginsin suclfa way 'that when the charging current passes through the choke coil it will have only small effect on account of its saturation, while with the reverse cur; rent --r-0m the battery which will therefore demagnetize the choke, a high inductive impedance will be caused and therefore a high choking effect, as can be'seen from Fig. 3. This reverse current will therefore be so'small that it can pass through the rectifying apparatus without any danger'.-,

Having believe to be new and desire tosecure and protect by Letters Patent of' the United States is I e 1. An arrangement for preventionof back currents in a battery charger, comprising a saturated choke coil with a separate magnetization means for flow freely on accountof the saturation, while a discharge current will meet with high impedance on accoun-t of demagnetia rectifying arrangement and means for prevention of reverse current, said means lncludmg a choke c011, a magnetizing winding on said choke coil, supply connections described my invention, what .I-

.ternatingcurrent supply and comprising a m'echanical rectifier, a choke coil, a core for the choke coil and a winding supplied'by arranging the choke coil so that the charging current will 7 ulator' connected to said magnetizing winding and a blockingcoil'in series with 'said magnetizing winding to protect the source of supply to said winding. I

3. A battery charging device utilizing alternating current supply and comprising a mechanical rectifier, a choke coil, a core for the choke-coil and a winding supplied by battery current to saturate said core, the direction of said winding being such that any current tending to flow from the battery to ward the'alternating current supply would oppose thesaturation due to saidvwinding. 4. A battery charging device utilizing albattery current-to saturate said core, the direction of said winding being such'thatany current-tending to flow from the battery toward the alternating current supply would oppose the saturation .due to said windingand means for regulating the current through said choke coil.

In testimony whereof I have 'aflixed my 55- signature.

KARh SCHMIDT.- f 

